A battery cell stores energy which can be output as electrical power.
A rechargeable battery cell may be recharged by providing electrical power to the battery cell. The battery cell stores energy which is output as electrical power as the battery cell discharges.
When a battery cell is incorporated into an apparatus, the apparatus when switched on may provide on a display an indication of the energy currently stored in a battery cell. This uses some of the battery cell's energy
However, it is inconvenient to have to switch on the apparatus to assess the energy currently stored in a battery cell.